North Korea's decision not to carry out a sixth nuclear test or a major missile launch in connection with its key anniversaries in April, contrary to widespread predictions, could herald a return to behind-the-scenes diplomacy between Pyongyang and Washington.

U.S. President Donald Trump's administration has not shown any intention to drop its mantra that all options, including a military strike, are on the table.

But a statement released by the U.S. administration on Wednesday after an extraordinary classified briefing on North Korea for the entire Senate made no specific reference to military options.